Your company here — click to reach over 10,000 unique daily visitors

joy - Man Page

Global array of joystick state information. Allegro game programming library.


#include <allegro.h>

extern JOYSTICK_INFO joy[n];


Global array of joystick state information, which is updated by the  poll_joystick() function. Only the first num_joysticks elements will  contain meaningful information. The JOYSTICK_INFO structure is defined as:

   typedef struct JOYSTICK_INFO
      int flags;                       - status flags for this
      int num_sticks;                  - how many stick inputs?
      int num_buttons;                 - how many buttons?
      JOYSTICK_STICK_INFO stick[n];    - stick state information
      JOYSTICK_BUTTON_INFO button[n];  - button state information

The button status is stored in the structure:

   typedef struct JOYSTICK_BUTTON_INFO
      int b;                           - boolean on/off flag
      char *name;                      - description of this

You may wish to display the button names as part of an input  configuration screen to let the user choose what game function will be  performed by each button, but in simpler situations you can safely assume  that the first two elements in the button array will always be the main  trigger controls.

Each joystick will provide one or more stick inputs, of varying types.  These can be digital controls which snap to specific positions (eg. a  gamepad controller, the coolie hat on a Flightstick Pro or Wingman  Extreme, or a normal joystick which hasn't yet been calibrated), or they  can be full analogue inputs with a smooth range of motion. Sticks may  also have different numbers of axes, for example a normal directional  control has two, but the Flightstick Pro throttle is only a single axis,  and it is possible that the system could be extended in the future to  support full 3d controllers. A stick input is described by the structure:

   typedef struct JOYSTICK_STICK_INFO
      int flags;                       - status flags for this
      int num_axis;                    - how many axes do we
                                         have? (note the misspelling)
      JOYSTICK_AXIS_INFO axis[n];      - axis state information
      char *name;                      - description of this

A single joystick may provide several different stick inputs, but you can  safely assume that the first element in the stick array will always be  the main directional controller.

Information about each of the stick axis is stored in the substructure:

   typedef struct JOYSTICK_AXIS_INFO
      int pos;                         - analogue axis position
      int d1, d2;                      - digital axis position
      char *name;                      - description of this axis

This provides both analogue input in the pos field (ranging from -128 to  128 or from 0 to 255, depending on the type of the control), and digital  values in the d1 and d2 fields. For example, when describing the X-axis  position, the pos field will hold the horizontal position of the  joystick, d1 will be set if it is moved left, and d2 will be set if it is  moved right. Allegro will fill in all these values regardless of whether  it is using a digital or analogue joystick, emulating the pos field for  digital inputs by snapping it to the min, middle, and maximum positions,  and emulating the d1 and d2 values for an analogue stick by comparing the  current position with the centre point.

The joystick flags field may contain any combination of the bit flags:

JOYFLAG_DIGITAL This control is currently providing digital input.

JOYFLAG_ANALOGUE This control is currently providing analogue input.

JOYFLAG_CALIB_DIGITAL This control will be capable of providing digital input once it has  been calibrated, but is not doing this at the moment.

JOYFLAG_CALIB_ANALOGUE This control will be capable of providing analogue input once it has  been calibrated, but is not doing this at the moment.

JOYFLAG_CALIBRATE Indicates that this control needs to be calibrated. Many devices  require multiple calibration steps, so you should call the  calibrate_joystick() function from a loop until this flag is cleared.

JOYFLAG_SIGNED Indicates that the analogue axis position is in signed format, ranging  from -128 to 128. This is the case for all 2d directional controls.

JOYFLAG_UNSIGNED Indicates that the analogue axis position is in unsigned format,  ranging from 0 to 255. This is the case for all 1d throttle controls.

Note for people who spell funny: in case you don't like having to type  "analogue", there are some #define aliases in allegro/joystick.h that will allow you to write "analog" instead.

See Also

install_joystick(3), poll_joystick(3), num_joysticks(3), calibrate_joystick(3), calibrate_joystick_name(3), exjoy(3)

Referenced By

calibrate_joystick(3), calibrate_joystick_name(3), exjoy(3), JOYSTICK_AXIS_INFO(3), JOYSTICK_BUTTON_INFO(3), JOYSTICK_INFO(3), JOYSTICK_STICK_INFO(3), num_joysticks(3), poll_joystick(3).

version 4.4.3 Allegro manual